1. Field of the Invention
The present invention relates generally to a viscous fluid coupling device. In particular, the present invention is concerned with a dual face wiper of a viscous fluid fan clutch for a vehicle.
2. Statement of the Related Art
A thermostatically-controlled viscous fluid clutch assembly for driving and rotating a vehicle cooling fan is well-known. A multi-bladed fan is removably secured to a body of the clutch assembly. The fan and clutch assembly are Installed between an accessory pulley of a vehicle engine (typically the water pump pulley) and a radiator. The clutch assembly drives the fan at high speeds close to input speed when cooling is required and permits the fan to rotate at low speeds when cooling is not required. Thermostatic control of the fan through the clutch assembly reduces the load on an engine and the noise caused by fan rotation, resulting in horsepower gain and improved fuel economy.
Generally, a clutch plate, housed within the clutch assembly, having lands and grooves is mated to the body having complementary lands and grooves. A pump plate separates a pair of internally-contained chambers, a receiving chamber and a collecting chamber, from a reservoir. Gates in the pump plate permit selective flow of a viscous fluid from the reservoir to the receiving chamber and Into a shear zone between the lands and grooves of the bodY and clutch plate. Fluid shear in the lands and grooves transfers input torque from the clutch plate to drive the body and the attached fan.
When cooling is not required, gates in the pump plate are closed and the fluid in the shear zone is pumped into the receiving chamber. Orifices in the pump plate permit passage of the fluid from the receiving chamber into the reservoir. The removal of a majority of the fluid from the shear zone substantially reduces the shear between the clutch plate and the body, thereby substantially reducing the rotation of the fan.
It is well-known to provide wiper elements on a surface of the pump plate in communication with the receiving chamber. A wiper, which can be formed as a thin, flat element, is secured to the pump plate (usually by welding) adjacent each pump plate orifice. In other embodiments, a wiper may be formed by stamping a cylindrical projection in a pump plate. As the wiper encounters fluid in the receiving chamber, an increase in fluid pressure occurs as the wiper creates a fluid dam. The increase in fluid pressure results in increased fluid flow through a pump plate orifice.
To further enhance the pumping ability of a wiper, it is well-known to provide a "scoop" and surface on a wiper. A scoop end surface is a curved surface of the wiper positioned adjacent a pump plate orifice. The curved surface includes an inlet or "bay" portion which receives oncoming fluid in the collecting chamber and creates a fluid dam.
In conventional fan clutches, the wiper must be secured to the pump plate so that the scoop surface encounters oncoming fluid. If a wiper is improperly positioned on the pump plate so that the scoop surface does not encounter oncoming fluid, then the advantages of the scoop surface will not be realized.
Fan clutches are designed to be rotated in either a clockwise or counterclockwise direction, depending upon the application. A critical aspect of conventional fan clutch assembly includes the inclusion of a pump plate having a wiper scoop surface oriented for the proper direction. Separate pump plate inventories are maintained for clockwise and counterclockwise clutch assemblies. Careful attention is employed to ensure that the proper pump plate is assembled with the respective assembly.
The art continues to seek improvements. It is desirable that a viscous fluid clutch assembly provide thermostatic operation of a fan when cooling is required. Furthermore, it is desirable that a clutch assembly be capable of either clockwise or counterclockwise rotation, depending upon the requirements of the application.